Pertussis toxin (PT) plays a major role in the pathogenesis of pertussis. Active immunization against PT provides a high level of protection against clinically severe infection. In experimental models, antibodies (Abs) to PT can reverse toxicity from experimental B. pertussis infection or from PT challenge even when administered one to two days after the challenge. These observations suggest that PT does not immediately become irreversibly associated with its target tissues. The hypotheses underlying the proposed experiments are 1) that pertussis antitoxin will ameliorate systemic toxicity associated with severe pertussis in humans by neutralizing PT free in the respiratory tract, the circulation, or reversibly bound to tissues, and 2) that pertussis antitoxin will prevent the development of clinical pertussis in contacts. We will evaluate polyclonal and monoclonal Abs to PT for antitoxin activity in vitro, for protection from PT or B. pertussis challenge in experimental models and for therapeutic benefit in children with severe pertussis. The specific goals of this proposal are: 1. To evaluate the adult Ab response to pertussis toxoid by measuring its Ig class and subclass composition, specificity for neutralizing epitopes on the toxin, and function in inhibiting the binding, enzymatic and holotoxin activities of the toxin. 2. To determine which assay(s) identify Abs to PT with the highest activity in protecting animals from PT-induced toxicity or from B. pertussis infection. 3. To prepare a human Pertussis Immune Globulin for intravenous administration (P-IGIV) from plasma donors immunized with pertussis toxoid and selected for high levels of pertussis antitoxin activity. 4. To evaluate the toxin binding and toxin neutralizing activities of P- IGIV and to compare them with selected monoclonal neutralizing Abs to PT and to conventional IGIV from unimmunized donors. 5. To evaluate importance of dose and timing of P-IGIV in protecting mice from PT challenge in aerosol B. pertussis challenge. 6. To evaluate the safety and pharmacology of P-IGIV in children with suspected or documented pertussis. During later years of this proposal, we will design clinical studies for the evaluation of P-IGIV in the treatment of severe pertussis in hospitalized children and of an intramuscular pertussis immune globulin for the treatment of milder pertussis in non-hospitalized patients. Because the therapeutic options for treating severe pertussis in children are limited to supportive care and erythromycin (which has little effect on the clinical course of established pertussis), the evaluation of new therapies for pertussis such as passive immunization has practical importance. The results of these experiments will also enhance our understanding of the role of PT in the pathogenesis of pertussis and of the human Ab response to this important molecule.